In existing clean air fan filter modules the fan is mounted primarily within the final filter assembly which compresses the air within the final filter assembly resulting in pressures above the final filter higher than necessary to pass air through the final filter. By mounting the fan and vanes substantially within the interior walls of the bifurcated conical ring the same volume of air may be supplied to the final filter assembly at a lower fan speed with less energy consumption and less noise, than in systems where the fan and vanes are located primarily in the final filter assembly. The centrifugal fan is used in conjunction with a speed control to achieve the desired air throughput through the final filter assembly. The higher deflected air pressure produced by mounting the fan and vanes substantially within the interior walls of the bifurcated conical ring also enables the fan motor mount assembly to be used in association with filters which create more back pressure than conventional final filters.
The air pre-filter assembly has been designed with side entry of incoming air to overcome two of the disadvantages of top entry pre-filters. When clean air fan filter modules are mounted in rooms where there is little space above the structure in which the clean air fan filter module is mounted, the air supply to the pre-filter assembly may be interfered with by the ceiling or structure. The use of a solid top on the pre-filter assembly of the invention combined with the larger relative surface area on the sides of the pre-filter assembly having apertures defining openings overcomes resistance to air flow found in top entry pre-filters in confined vertical spaces.
Another advantage of a side entry pre-filter is that a substantial increase of the pre-filter intake surface area may be created than is possible with an air pre-filter having the air entry to the pre-filters immediately above the air inlet to the fan motor mount assembly. In the pre-filter assembly of this invention the air pre-filter apertures and material are attached over the openings in the sides of a continuous top plate having apertures defining openings. The remaining sides and the top of the pre-filter assembly do not have apertures defining openings. Increasing the surface area of the filter material in contact with the air decreases the static pressure through the filter material and the amount of energy necessary to pull the air through the pre-filter material.